The general aim of this project is to determine the molecular and quantitative genetic basis of mating behavior in Drosophila. The specific aims are to map with high resolution the quantitative trait loci (QTL) responsible for intra-specific variation in courtship initiation time and time to copulation in Drosophila melanogaster; and to map QTL associated with pre-zygotic reproductive isolation between D. mauritiana and D. simulans. Previously, I mapped QTL responsible for variation in male mating behavior between two D. melanogaster strains. Deficiency and recombination mapping will be used to map these QTL with high resolution, and complementation testing will be used to identify candidate genes responsible for naturally occurring variation in behavior. The number, map positions and effects of QTL responsible for ethological divergence between species will be determined by associating mating behavior with polymorphic molecular markers in interspecific backcross hybrids.